The molecules and mechanisms that control axon guidance are highly conserved among flies, worms and vertebrates. In the Drosophila visual system, retinal axons play a critical role in orchestrating the development of the targets to which they project. Understanding the mechanisms which guide retinal axons to topographically correct sites within the Drosophila brain is likely to contribute to an understanding of these processes in vertebrates. Recently, Drosophila Eph receptor tyrosine kinase (Dephr) has been implicated in retinal axon guidance. We will examine Dephr function in this process using mutant receptors introduced as transgenes and loss of function conferred by RNAi genetic interference. Screens for modifier mutations that rescue Dephr phenotypes may allow us to uncover novel elements of the Dephr signaling pathway. This study may provide novel insights into the mechanisms by which retinal axons are guided to appropriate target fields as well as uncover components of the signaling pathway utilized by the Eph family of receptors.